This invention relates to electric rotating machines and more particularly to self-starting synchronous and stepper motors.
There has been developed a class of electric motors which are compact in size and extremely efficient. Representative motors of this type are disclosed in Arthur W. Haydon U.S. Pat. Nos. 3,495,113 granted Feb. 10, 1970, 3,495,111 also granted Feb. 1, 1970 and 3,564,214 granted Feb. 16, 1971; Arthur W. Haydon and John J. Dean patent 3,770,998 granted Nov. 6, 1973; and Arthur W. Haydon copending application Ser. No. 438,761 filed Feb. 1, 1974, now U.S. Pat. No. 3,909,646 granted Sept. 30, 1975. To achieve unidirectional self-starting characteristics, motors of this type commonly include shading devices for selected ones of the stator poles and a nonuniform air gap between the stator poles and the rotor, such that upon energization of the field coil of the motor, the rotor uniformly and consistently begins its rotation in a given direction.
Electric motors including those of the foregoing type in a number of instances need to operate reliably for extended periods of time in a sealed or inaccessible location. Particularly under such conditions, the motors advantageously should be of simple construction with a minimum number of parts, because additional parts often create potential sources of failure. In many cases, as in air-borne or space vehicles, the weight of the motor also is a consideration.
Additionally, the motors often are employed with auxiliary apparatus under conditions in which the motor is designed to be discarded and replaced, after a period of time, rather than repaired. The design of the motor accordingly should be such that it may be readily plugged in and removed from a mating receptacle on the apparatus, and since each additional part usually represents an added item of cost, it is desirable to minimize the number of parts.
To further improve the overall compactness and efficiency of the motors and at the same time lower their cost to the consumer, it would also be desirable to simplify the design of the field coil and cooperating structure. However, attempts to eliminate such parts as shading rings, for example, often resulted in a motor that heretofore was not consistently and reliably self-starting in a given direction. In addition, the fine wire size and large number of turns in the coils of prior motors designed for operation at, say, 115 volts at 1 watt, resulted in a coil which was too expensive for certain applications.
Difficulties also were encountered in the assembly of such previous motors, and particularly in the successive steps necessary to secure the electrical leads to the coil and to provide for suitable connectors externally of the housing of the motor in order to attach the leads to a source of power.